import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  String checkValue ="A";

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Row(
          children: <Widget>[
            Radio<String>(
                value: "A",
                groupValue: checkValue,
                onChanged: (v) {
                  setState(() {
                    checkValue=v;
                  });
                  print(v);
                }),
            Radio<String>(
                value: "B",
                groupValue: checkValue,
                onChanged: (v) {
                  setState(() {
                    checkValue=v;
                  });
                  print(v);
                })
          ],
        ),
      ),
    );
  }
}
